This invention relates generally to semiconductor transistors. In particular, the invention relates to heterojunction bipolar transistors. Heterojunction bipolar transistors (HBTs) offer a much higher speed of operation than the more prevalent metal oxide semiconductor field effect transistors (MOSFETs) or even conventional homojunction bipolar transistors, e.g., pnp or npn silicon transistors. Because HBTs offer high speed, high current driving capability, and low 1/f noise levels, HBTs are becoming popular for use as integrated switching devices and power amplifier devices in wireless communication systems and subsystems, satellite broadcast systems, automobile collision avoidance systems, global positioning systems, and other high frequency applications. One application in which HBT use continues to increase is in the design and manufacture of wireless electronic devices, such as wireless telephones and other like electronic devices that are capable of communicating with a network in a wireless manner.
As with all wireless electronic devices, the output power characteristics of a power amplifier along with the amplifier's ability to withstand large voltage swings is a concern to both the designer and consumer of the portable wireless device. For example, it is desirable to maximize output power and reliability of the wireless electronic device by providing the device with one or more HBT power amplifiers that maximize power performance and high frequency performance and thus, broad bandwidth operation capability. By providing the wireless electronic device with an HBT power amplifier having an improved on-state breakdown capability often results in a desirable increase in the reliability of the amplifier by improving the ability of the amplifier to withstand large voltage swings. As such, the use of an HBT power amplifier having an improved on-state breakdown capability improves output power characteristics and the ruggedness or the ability of the amplifier to withstand large voltage swings benefits a mobile telephone supporting a digital wireless telephone standard, such as the global system for mobile communication (GSM). Moreover, it is desirable to increase the reliability of an HBT power amplifier provided in a wireless electronic device by lowering the intensity of electric fields within a selected region of the HBT power amplifier.